Calcium is the most abundant mineral in your body, 99% of which is found in your bones and teeth — after all, its main purpose is to build and maintain strong bones and teeth. The remaining 1% of your calcium is used for blood vessel dilation and constriction, muscle contraction, nerve transmission, and hormone secretion.
During pregnancy, calcium stores in the expecting parent's body are the main source of the nutrient for the fetus. A baby's bones grow the most rapidly in the third trimester, and during this time an estimated 200-250 mg is transferred to the fetus per day. But here’s where the calcium story gets really interesting: The Dietary Reference Intake (DRI), which is the amount you need to consume on a daily basis, is the same for pregnant people and non-pregnant people with ovaries — despite the extra demand on a pregnant person's body.
All adults with ovaries are advised by the National Institutes of Health (NIH) to get 1,000 mg per day of calcium — the American College of Obstetricians and Gynecologists (ACOG) recommends the same for pregnant people and during lactation (whether or not you're breastfeeding/chestfeeding). The DRI for calcium only increases to 1,200 mg post-menopause.
The exact prevalence of calcium deficiency is a little unclear because of conflicting numbers from various (often outdated) sources, but the Office of Dietary Supplements at the National Institutes of Health doesn't list people with ovaries of reproductive age as one of the populations most affected. That said, many people may be slightly deficient: Recent data shows this deficit is around 100 mg per day for people with ovaries in the 20-39 age bracket. In the end, it's important to keep an eye on your intake of calcium-rich foods and consult with your doctor to see if supplementation before, during, and after pregnancy is right for you.
Why you may not need more calcium while pregnant
What’s unique about calcium when compared to other vitamins and minerals is that your calcium status is less vulnerable to dietary fluctuations. Instead, your bone tissue is constantly undergoing cycles of breakdown and repair, depositing and absorbing calcium as needed to keep circulating levels constant.
During pregnancy, your body continues this vigilant control over calcium levels with the following adaptations:
- Your ability to absorb calcium from food nearly doubles during pregnancy. This means you can eat the same amount of calcium but more of it will actually get into your body (rather than pooped out).
- On an as-needed basis, bone tissue, which stores calcium, will break down to free up more of the nutrient. (If you're not getting adequate calcium intake through food or supplementation, that can decrease bone mass because your body's relying on bone tissue for the nutrient.)
- Increased estrogen levels during pregnancy counteract this breakdown by helping to rebuild bone mass. In the long term, bone mass helps prevent osteoporosis and bone loss.
These inherent processes that keep calcium levels under tight control doesn't mean you can ignore calcium — you still need to get the recommended 1,000 mg per day, from food or supplementation. And other bone-building nutrients that work synergistically with calcium, like vitamin D, can help with calcium absorption and bone mineralization.*
Got milk?: Getting your calcium intake from food
How tricky it may be to get your 1,000 mg of calcium largely depends on your relationship with dairy and other calcium-rich foods. Dairy foods are one of the best sources of calcium, but it's not the only source.
Here are some of the top sources for calcium, and the approximate amount they provide:
Calcium per serving
|~400 mg||~300 mg||~200 mg||~100 mg|
Orange juice (fortified w/ calcium)
If you eat 2-3 servings of dairy most days — like cereal with milk in the morning, a yogurt cup as a snack, and pizza, lasagna, or enchiladas for dinner — you likely have your daily dietary calcium intake covered.
For people who are already meeting their dietary calcium requirement, randomized controlled trials (RCT) including pregnant women don't show that calcium supplementation during pregnancy improves maternal bone health (likely because calcium is so tightly regulated by the inherent physiological processes described above).
When calcium intake from food might not be enough
If you're lactose intolerant or avoid dairy products for other reasons, getting calcium from food requires a little more dedicated attention — and supplementation could be beneficial for you.* An estimated 85% of people of Asian descent and 50% of Black Americans are lactose intolerant, per the Office of Dietary Supplements. For people with darker skin tones, lower levels of vitamin D (higher melanin production blocks UV rays the body uses to make vitamin D) might also impact calcium absorption — though for Black people in particular, vitamin D deficiency may not actually lead to adverse outcomes in bone health.
All of this said, if you're eating the non-dairy foods shown in the table above — fortified options (like tofu, breakfast cereal, soy milk, and OJ), dark leafy greens (like kale and bok choy), chia seeds, or canned sardines/salmon — then you’re likely getting enough calcium. If, however, you’re relying on non-fortified, plant-based sources of calcium (in addition to or in place of supplementation), understanding the absorbability of the calcium in those foods is key.
Calcium absorption and oxalic acid
Oxalic acid is a naturally occurring compound found in many plants (like spinach) that binds calcium and prevents absorption. Often, foods may be listed as a rich source of calcium, but that calcium is not readily available for absorption. Foods high in calcium but also high in oxalic acid include:
- Collard greens
- Sweet potatoes
Supplementing your calcium intake
If you decide to supplement with calcium, you have the option of taking a stand-alone supplement or a prenatal multivitamin that includes calcium to meet your nutritional needs through future pregnancy. (An important thing to note, though, is that many prenatal multivitamins don't have calcium in them — including the Modern Fertility Prenatal Multivitamin.)
Whether you're looking for a prenatal with calcium on the label or you're planning on taking a separate supplement, there are a few considerations to keep in mind:
- Calcium can block the absorption of iron, so you want to take in the nutrients at different times throughout the day. For example, if your main source of iron is steak at dinnertime, take the calcium supplement in the morning. Similarly, if your prenatal includes iron, take it in the morning and take your calcium supplement in the evening.
- Consider the form of calcium supplement you take.
- Calcium carbonate is the most common form found in supplements and is best absorbed when taken with food. The carbonate form is also the most likely to cause gastrointestinal (GI) issues, like constipation, gas, and bloating.
- Calcium citrate is less likely to cause GI issues and can be taken with or without food.
- Absorption of calcium supplementation maxes out at ~500 mg. If you’re taking calcium supplements to meet the DRI, you'll need to split that into multiple doses throughout the day.
- Vitamin D is essential for calcium absorption and is included in most top-selling prenatal vitamins.
Why Modern Fertility left calcium out of their prenatal
For many of the reasons outlined above, you won't find calcium in the Modern Fertility Prenatal Multivitamin. Since each capsule can only hold so much, creators of prenatals (and other supplements) will often weigh the pros and cons of incorporating individual nutrients. A lot of these decisions come down to balancing what people are likely already getting from food and what nutrients are at a higher risk of deficit.
Instead of adding an extra capsule — one that would have to be taken at a separate time from the other two to avoid interference with iron absorption, the most common micronutrient deficiency — Modern Fertility opted for the calcium booster vitamin D. Vitamin D increases the nutritional goodness you can get from eating your pick of many calcium-rich foods.*
If you start taking the Modern Fertility Prenatal Multivitamin and want to add a calcium supplement to your daily routine, talk to your healthcare provider first. They may recommend taking your calcium dose at a different time from your prenatal.
So, should you take a calcium supplement or prenatal multivitamin with calcium?
Ultimately, deciding whether or not to supplement your calcium intake before and during pregnancy depends on your body and unique circumstances. If you're not sure what's best for you, you can always talk to a health professional to figure out the right nutritional plan to support your reproductive future.
|*This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.|